1. Field of the Invention
The present invention relates to an impedance conversion circuit preferably for use in an antenna device and other devices. In particular, the present invention relates to an impedance conversion circuit that provides matching in a wide frequency band, and to a communication terminal apparatus equipped with the impedance conversion circuit.
2. Description of the Related Art
In recent years, communication terminal apparatuses, such as mobile phones, may require compatibility with communication systems, such as a GSM (registered trademark) (Global System for Mobile communication), DCS (Digital Communication System), PCS (Personal Communication Services), and UMTS (Universal Mobile Telecommunications System), as well as a GPS (Global Positioning System), a wireless LAN, Bluetooth (registered trademark), and the like. Thus, antenna devices for such communication terminal apparatuses are required to cover a wide frequency band of 800 MHz to 2.4 GHz.
Antenna devices for a wide frequency band typically have a matching circuit for each frequency band (PCT Japanese Translation Patent Publication No. 2003-536338), and switch an electrical length of an antenna with an active element (Japanese Unexamined Patent Application Publication No. 2008-118535).
However, in the antenna devices disclosed in PCT Japanese Translation Patent Publication No. 2003-536338 and Japanese Unexamined Patent Application Publication No. 2008-118535, since it is necessary to design the antenna pattern for every terminal, the antenna design becomes time consuming; and since such antenna devices also require an active element such as a switching circuit in order to switch a signal path, the circuit configuration is likely to be complicated.